Bestseller le Carré (The Constant Gardener ) brings a light touch to his 20th novel, the engrossing tale of an idealistic and naïve British interpreter, Bruno "Salvo" Salvador. The 29-year-old Congo native's mixed parentage puts him in a tentative position in society, despite his being married to an attractive upper-class white Englishwoman, who's a celebrity journalist. Salvo's genius with languages has led to steady work from a variety of employers, including covert assignments from shadowy government entities. One such job enmeshes the interpreter in an ambitious scheme to finally bring stability to the much victimized Congo, and Salvo's personal stake in the outcome tests his professionalism and ethics. Amid the bursts of humor, le Carré convincingly conveys his empathy for the African nation and his cynicism at its would-be saviors, both home-grown patriots and global powers seeking to impose democracy on a failed state. Especially impressive is the character of Salvo, who's a far cry from the author's typical protagonist but is just as plausible. (Sept.)